24.11.2006 19:50

There was still an open problem on my list: Namely, that my PATH variable is truncated if I use the fingerprint reader to login in gdm. I did not really solve the problem. That is, I still don't understand why the path is set differently depending on whether I login with password or fingerprint. I don't understand actually at all where the PATH is set in gdm. There are these lines in "/etc/gdm/gdm.conf"

# Default path to set. The profile scripts will likely override this value.
# This value will be overridden with the value from /etc/default/login if it
# contains "ROOT=(pathvalue)". #DefaultPath=/usr/local/bin:/usr/local/sbin:/sbin:/usr/sbin:/bin:/usr/bin:/usr/bin/X11:/usr/games

I fixed my problem by uncommenting the line starting with DefaultPath. So apparently if this line is there, it sets the default path in gdm, but if not? I don't have the "/etc/default/login" memtioned above. There seems to be some confusion where the PATH is really set. I found similar problems like mine (not involving fingerprint readers though) on the web. But no answer was really satisfactory. What appears are the usual suspects:

/etc/environment
~/.bash_profile
~/.basrc


Or similar things for other shells. What I know by now, is that out of these three only "~/.bashrc" is read by gdm. If you want to make local changes to the PATH do it there. And if you want to do global changes do them in "/etc/gdm/gdm.conf" to make sure it is applied.

23.11.2006 18:54

There was this fancy paper yesterday on the arXiv. So it seems that the kids will soon be playing with extreme QCD instead of silly shooting war games. Of course, this will help them becoming enthusiastic scientists instead of engaging in some stupid killings in schools. ;-)
And there is some really fancy stuff you can experience. I have started to cook up some ideas. What about diving deep into the interior of a Wilson fermion "fractal".

22.11.2006 13:36

Es ist ja so einfach, warum ist mir das nicht früher eingefallen?
Wenn man so Anrufe von Call Center Fritzen bekommt, die einem irgendeinen Scheiss andrehen wollen oder irgendeine blöde Befragung durchführen wollen, muss man einfach antworten: "Oh sorry, do you speak English?" Die Dänen legen sofort wortlos auf, dann muss es ja auch bei den Deutschen klappen, denn die können ja im Schnitt schlechter Englisch.

16.11.2006 13:59

Sometimes I like the EU. Yes, it's a good thing to have additional tolls on goods from countries that do not respect the Kyoto protocol, and yes it's only a fair thing to have the flight industry pay for climate damage they cause and finally yes, it's also a thing to set an ultimatum on Microsoft.

14.11.2006 17:13

aber Waelder in den noerdlichen Breitengraden, wo die Industrienationen liegen, sind nunmal nicht zu vergleichen mit den tropischen Waeldern in Brasilien, Indonesien etc.
Wenn unsere Waelder wachsen und jene schrumpfen, dann heisst das ja einfach, dass wir unseren Waldkonsum exportiert dahin exportiert haben, wo die Oekosysteme labiler sind und einmal gerodete Flaechen schwieriger wieder zu regenerieren. Wenn man hier die Bewegung umkehren kann heisst das noch lange nicht, dass das auch in Brasilien geht. Und ein Regenwald ist von Natur aus vielfaeltiger und artenreicher und daher viel wertvoller, als was wir hier so haben.
Ausserdem nimmt zum Beispiel in der Schweiz die Waldflaeche auch auf Kosten von extensiv bewirtschaftetem Kulturland zu, was eher negative Folgen auf die Artenvielfalt hat.

11.11.2006 12:32

Imagine a particle moving under the unfluence of a central force. Then it's angular momentum is conserved, the particle moves on a two dimensional plane. Like the planets orbiting the sun. Nobody ever claims that you should quantify over these planes. Of course not that would be utterly silly. It's simply a constraint in the motion, induced by the fact that the force acts in a particular way.

If you have a closed relativistic string which moves in D dimensions and one of them is compact. Say you have a rubber band which moves very fast in a tube) then it turns out that there is a thing called T -duality which means essentially that your rubber band in the tube of radius R is equivalent to a rubber band in a tube of radius 1/R. Now you cut the rubber band and get an open string, you still want this T-duality to hold. I turns out, that the ends of your open string are confined to D-1 dimensions. They cannot move around the tube. Hence says the string theorist (at least that is how I understand the arguementation in Johnsons book) there is a thing, which is this D-1 dimensional object.

Caveat: I do a lot of string bashing here, because I have to read that book for a reading course here. The reason why I engaged in this was, that I thought it would help me to understand it a little better. The truth is it doesn't really. I just find it annoying. I have to give a presentation next week and I promised myself, it will be the last bit I do for it.
I have very strong prejudices against string theory which to a large part come from this incredibly over enthusiastic and uncritical attitude towards it. Together with the fact that there is no evidence for it to be true whatsoever. I don't have anything against people persuing it and it might turn out to be true eventually, but up to now it is completely misleading to talk in a way about as if it was well established. And that is what many string theorists do.
Remember this is an inductive science.
Also, I believe that string theory has already missed many of the goals it's proponents set out to achieve. Where have the elegance, the simplicity and especially the uniqueness gone? After leaving half a year in a string world, I wouldn't been amazed anymore if anybody claimed one day that in a certain string theory there are actually unicorns, and the strings are just the hair of their tails. I have the impression that string theory is so general or "rich" that in the end it cannot make any predictions at all. Whatever physicist will find out there in the world, there will be a string theory that describes it. And they will claim victory. But the more general a theory, the less interesting is it for obvious reasons, it doesn't exclude anything and hence doesn't make any predictions.
My feeling towards it is actually even worse: I am not even convinced that there is a possible world, where string theory is true.

10.11.2006 12:05

"the computation is complicated enough that at some stage computers must be used."

(from Zwiebach, A first course in string theory)

09.11.2006 16:51

CUP is quite a renowned and big editing house for accademic literature. Their books are reasonably expensive so I wonder why the can't invest a little in a good lectorate. I own two books from the "Cambrigde monographs on mathematical physics" series. One is "the Montvay Muenster", the bible in lattice field theory, the other one is Clifford Johnsons book on D Branes. To be honest,I love neither of them, but at t least the bible is unreplaceable. Both are not very clear in their argumentation, which is the authors fault. But Montvay Muenster has such a horrible lazy-style latex typesetting that it is unpleasant to read, just for that. And Johnsen is packed with typos, sometimes in formulae, where of I probabely only find 1/3, but also in text. Some of them a simple spell checker would notice. That's embarrassing.

yeah, I know there are also a lot of typos on this site, but I don't sell you the stuff for lots of money, right?

02.11.2006 11:13

I am sure that if there were a strange regularization method showing that string theory is in fact consistent only in dimensions, there would be a lot of people claiming that there really are dimensions. First of all it must be right, because there is in it. And the universe would just be an extremely awful fractal, like these horrible shapes I used to dream of in my childhood when I had high fever. Some surfaces so rough and warped that you felt sick of. Oh yes and there would be a duality connecting this universe to the other surfaces I saw in those dreams. They were so smooth that you equally felt sick of. Both of them transformed endlessly into each other.
Hoho, I really should construct such a theory. Then we could form a club of those privileged people that can see the whole universe in their dreams, my sister would also be member, and wo. Who join?